Ball screw apparatus

Abstract

A ball screw apparatus having a revolving position detector for detecting revolutions of a ball screw nut and a ball spline nut and a number-of-revolutions altering means for issuing a command to decrement or increment the number of revolutions of the ball screw nut so that a difference between sets of revolution numbers becomes zero. In the ball screw apparatus, a driving motor is disposed in parallel with a driving shaft. An output of the driving motor is transmitted via a belt to each nut. When driving the motor in a clutch-off/brake-on state, only the ball screw nut is driven to revolve, and the driving shaft is slid in the axial direction. When driving the motor in a clutch-on/brake-off state, the two nuts revolve together, and the driving shaft is rotationally driven. A reduction ratio on the side of the ball screw nut is set equal to that on the side of the ball spline nut, whereby the two nuts synchronously revolve.

What is claimed is: 
     
       1. A ball screw apparatus comprising: a driving shaft formed with a ball screw groove and ball spline grooves; and   ball screw nut and ball spline nut arranged in side-by-side relationship in the axial direction and thread-attached to said driving shaft, said two nuts being connected to one driving motor to move said driving shaft in the axial direction and rotate said driving shaft about the axial line,   wherein said driving motor and said driving shaft are disposed so that the axial line of an output shaft of said motor is parallel with the axial line of said driving shaft, said ball screw nut is connected directly to said output shaft of said driving motor, said ball spline nut is connected to a rotation transmitting shaft connected via a clutch and a brake to said output shaft of said driving motor, a reduction ratio prescribed from said output shaft of said motor to said ball screw nut is set equal to a reduction ratio prescribed from said output shaft of said motor to said ball spline nut, and a revolving position detector for detecting revolutions of said ball screw nut and said ball spline nut is provided.   
     
     
       2. The ball screw apparatus according to claim 1, wherein said ball screw nut is connected via a first belt to a first pulley fixed to said output shaft, and said ball spline nut is connected via a second belt to a second pulley fixed to said rotation transmitting shaft. 
     
     
       3. The ball screw apparatus according to claim 2, wherein said revolving position detector is attached to said ball screw nut or said spline nut. 
     
     
       4. The ball screw apparatus according to claim 2, wherein said revolving position detector is attached to said rotation transmitting shaft. 
     
     
       5. In a ball screw apparatus including: a ball screw shaft formed with a ball screw groove and ball spline grooves; and   ball screw nut and ball spline nut attached via balls to said ball screw shaft, said ball screw nut being driven to revolve by a ball screw nut driving means, said ball spline nut being driven to revolve by a ball spline nut driving means, said two driving means being controlled in revolutions by a controller for controlling a predetermined number of revolutions independently,   the improvement comprising:   a ball screw nut number-of-revolutions detecting means for detecting the number of revolutions of said ball screw nut;   a ball spline nut number-of-revolutions detecting means for detecting the number of revolutions of said ball spline nut; and   a number-of-revolutions altering means for calculating a difference between sets of revolution numbers inputted from said two number-of-revolutions detecting means and issuing a command to decrement or increment the number of revolutions of said ball screw nut to said ball screw nut driving means so that the difference becomes zero.